Within the Telecommunications industry there are a number of initiatives to unbundle telecommunications services from the switches which provide them. Currently this is embodied by Intelligent Networking (IN) whereby the switches are provided with a number of trigger points at which they send a message to a Services Control Point in order to establish the next step in processing the call. Although IN has achieved many significant capabilities it is generally regarded as not being a sufficient separation of concerns to deal with the complexities that are now enabled by asynchronous transfer mode (ATM) networks.
In one approach to this problem, narrow band services are provided within the B-ISDN by mapping single 64 kb/s channels into ATM adaptation layer 1 (AAL1 VCs) and connecting them as switched VCs across the network, this creates the difficulty that the cell assembly delay of six milliseconds leads to a substantial revision of the network delay plans and a substantial increase in the requirement for echo cancellers, it also leads to the need for inter working between ISUP and B-ISUP signalling protocols leading to a substantial increase in the complexity of B-ISUP.
A general description of interworking of broad band and narrow band services using flexible signalling connections is given by Akihiro Sera et al. in Fujitsu Scientific and Technical Journal, Vol 28, No 2, Jan. 1, 1992, pages 150-159. This paper describes the enhancement of a digital switching system to evolve to a multi-service platform which can provide services for various media and interfaces.